G100UL, Swift, and the Long Goodbye to Leaded Avgas - The Fuel Transition Playing Out in the Oshkosh Exhibit Hangars

The aviation industry is working to eliminate leaded avgas by 2030 through a coalition called EAGLE, and at EAA AirVenture Oshkosh this July 2026 the competing replacement fuels are on display. Two credible unleaded fuels already exist - GAMI’s G100UL, approved fleet-wide, and Swift Fuels’ UL94, already pumping at a growing number of airports - but each solves only part of the problem. The transition is less about whether lead disappears than how, and it is the quietest consequential technology story in general aviation.

Why Does Avgas Still Contain Lead?

The blue fuel in nearly every general aviation tank is 100 low lead (100LL), which contains a small amount of tetraethyl lead. That lead is not an accident or an oversight - it is there because it works.

Lead is an exceptionally effective anti-knock agent. It lets fuel resist detonation, the destructive pre-ignition that can destroy a high-compression engine. A big-bore piston engine turning a prop at full power on a hot day desperately “wants” to knock, and lead prevents it.

Notably, 100LL is the last leaded transportation fuel in widespread use in the United States. Cars lost their lead decades ago, but the automotive fixes did not translate to a naturally aspirated aircraft engine running at 75% power for hours with no radiator and no margin for error.

Why Get the Lead Out Now?

Two reasons point in the same direction.

Health and environment. Lead is a neurotoxin with no safe level of exposure. The Environmental Protection Agency (EPA) issued an endangerment finding on leaded avgas emissions. That finding is a legal domino - once it is on the books, removing lead stops being a suggestion and becomes a countdown.

Supply chain fragility. The supply chain for 100LL is dangerously thin. There is essentially one producer of the specialized lead additive in the world, and very few refineries make the fuel. If any link in that chain breaks, a large portion of the piston fleet stops flying. Getting off lead means not betting the entire fleet on a single fragile supply line.

Who Are the Players Replacing Leaded Avgas?

The umbrella effort is EAGLE - Eliminate Aviation Gasoline Lead Emissions, a partnership between the Federal Aviation Administration (FAA) and industry. Its goal is to remove leaded avgas from the system safely by 2030. EAGLE is not a fuel; it is the roadmap and referee. The actual fuels come from competing companies.

GAMI (General Aviation Modifications, Inc.) of Ada, Oklahoma makes G100UL (the “UL” stands for unleaded). Rather than using the traditional industry fuel-specification process, GAMI pursued approval through the FAA’s Supplemental Type Certificate (STC) route - the same mechanism used to approve a new autopilot. It worked: G100UL earned approval covering, in principle, the entire fleet of piston airplanes and engines. A drop-in unleaded fuel requiring no engine modification, approved across the board, is a genuine engineering achievement.

But approval is not the same as availability. G100UL has faced friction - questions raised about material compatibility with certain sealants, paints, and older components, along with disputes over distribution and pricing. Some concerns have been hotly contested in the industry press. A fuel that is legal everywhere but available almost nowhere does not help the pilot on the ramp. That is not a dismissal of G100UL; it may well be a major part of the answer. It is simply the honest gap between a certificate on the wall and fuel in the tank.

Swift Fuels of Indiana took a different philosophy. Swift already sells UL94, a 94-octane unleaded fuel that is flowing at a growing number of airports today. The insight: a huge fraction of the fleet - Cessna 172s, Piper trainers, and other lower-compression engines - runs perfectly on 94 octane and never needed the full 100 to begin with.

The catch is the rest of the fleet. High-performance, turbocharged, high-compression engines - the big Continentals and Lycomings in six-seat singles and twins - genuinely need full octane. And here is the number that surprises people: that high-performance slice is a minority of the airplanes but burns the majority of the fuel. You cannot solve the problem by serving only the easy engines. Swift’s answer is a full-power unleaded fuel called 100R, working through the approval pipeline to cover the demanding engines UL94 cannot serve. Their strategy walks the fleet off lead in stages rather than one giant leap.

A third effort, a collaboration involving Phillips and Afton, is chasing the same full-replacement 100-octane target through the traditional specification process.

Which Unleaded Fuel Will Win?

From an engineering standpoint, there may not be a single winner. The system could end up with more than one unleaded fuel in service for a while, sorted by what your engine needs and what your local airport chooses to stock. GAMI’s pitch is “one fuel, approved for everyone now, solve distribution later.” Swift’s is “get the easy majority onto UL94 immediately, bring the high-octane fuel along behind it.” Both are credible.

Why Is This Harder Than It Was for Cars?

When automobiles went unleaded, the industry redesigned engines, added catalytic converters, and rolled changes out on new model years. Old cars aged out of the fleet within a decade or two.

Aviation cannot do any of that. The airplane you fly might have been built in 1978 and will still be flying in 2040. The fleet does not turn over. Engine designs are certified, frozen, and legally locked - you cannot simply retune them. And the stakes are not a hesitation at a stoplight; the consequence of getting fuel chemistry wrong is detonation at altitude, over terrain, with your family aboard.

So the bar is not “does this fuel mostly work.” The bar is: does it behave correctly in every approved engine, in every climate, at every power setting, stored in every kind of tank, for years, with zero surprises. That is an extraordinarily high bar, and aviation’s slowness here is not foot-dragging - it is the system proving the fuel before betting lives on it.

There is also a materials dimension pilots underestimate. Fuel does not just get burned; it sits. It soaks bladder liners and wets gaskets, O-rings, sealants, and fuel-gauge sending units. A new fuel with different solvent characteristics can interact with those materials differently over time - swelling a seal, or loosening decades of deposits and sending them toward a fuel filter. None of that shows up in a quick test flight. It shows up over seasons, which is exactly the long-tail risk careful testing is built to catch.

What Is the Realistic Timeline?

EAGLE is targeting 2030 for a safe, complete transition - but treat that as a target, not a promise, as you would any estimate for a hard engineering problem.

As of July 2026, the pieces already exist. UL94 is real and pumping today. G100UL is approved and fighting toward distribution. The high-octane full-replacement fuels are in the pipeline. What remains is the unglamorous work: fuel in every truck, tanks at every airport, and confidence in every mechanic and owner - earned one field and one season of real-world data at a time.

Why This Matters for Pilots

If you fly a lower-compression trainer, an unleaded future may already be available at your field via UL94. If you fly a high-performance or turbocharged airplane, you are waiting on the full-power fuels - G100UL, Swift’s 100R, or the Phillips/Afton effort - and their distribution. Either way, the fuel you burn is changing, and the smart move is to ask hard questions now: Will this affect my engine and its seals? What does my airplane actually need? What will it cost, and when can I buy it locally? Healthy skepticism is what keeps the transition honest, and honest is what keeps it safe.

Key Takeaways

• 100LL is the last leaded transportation fuel in widespread US use, kept for lead’s anti-knock protection of high-compression engines.
• Two forces are driving change: the EPA’s endangerment finding on lead emissions and a fragile supply chain with essentially one global producer of the lead additive.
• The EAGLE initiative (FAA + industry) targets 2030 for a complete, safe transition - a goal, not a guarantee.
• GAMI’s G100UL is approved fleet-wide but faces distribution and material-compatibility friction; Swift’s UL94 is already pumping for lower-compression engines, with 100R in the pipeline for high-octane needs.
• A minority of high-performance airplanes burns the majority of the fuel, so the transition is not complete until full-power unleaded fuel is widely available.